1. Field of the Invention
The present invention relates to a copper alloy for electrical or electronic parts such as a terminal, a connector, a relay and a bus bar, and in particular to a copper alloy for electrical or electronic parts which has superior strength (yield strength), electric conductivity, spring limit value, resistance property of stress relaxation, bendability and Sn plating property.
2. Description of the Related Art
Electrical equipment for cars is increasing. In such a situation, the number of connectors is also increasing in wire harness for connecting a battery or a controller to various electrical parts, actuators, sensors or the like. It has been demanded to make the connectors compact. Connectors mounted near an engine section are always under high temperature and high vibration environment based on the engine section. When a large electric current is sent particularly to a connector for supplying electric power, the connector generates heat by itself so that the temperature thereof rises up to a higher temperature. Therefore, it has been demanded that such a connector (particularly, a female terminal) has high reliability under the above-mentioned environment (that is, looseness does not arise).
As a material of a copper alloy connector for conventional cars or the like, Cuxe2x80x94Fexe2x80x94P alloys (CDA19400) or Cuxe2x80x94Mgxe2x80x94P alloys are known. The former alloys are alloys whose strength is improved by precipitation of Fexe2x80x94P compounds based on co-addition of Fe and P. There are also known an alloy whose migration-resistance is improved by further addition of Zn (see JP-A-No. 1-168830); an alloy whose resistance property of stress relaxation is improved by addition of Mg (see JP-A-No. 4-358033); and the like. The latter alloys are alloys whose strength and thermal creep property are improved by addition of both of Mg and P so as to improve tensile strength, electric conductivity and resistance property of stress relaxation (JP-B-No. 1-54420).
In order to make wiring connectors (particularly, female terminals) for electrical parts for cars compact and keep their reliability (keeping their contact/press power), it is necessary to make the strength (yield strength) and the spring property (spring limit value) of the material of the connectors higher. In order that looseness is not caused (that is, fitting power does not drop by passage of time) even if the connectors are kept at high temperature for a long time, it is necessary to improve their resistance property of stress relaxation. At the same time, it is necessary that their electric conductivity is improved to suppress self generation of heat. Besides, it is demanded that the above-mentioned material has superior formability (particularly, bendability) in order to form small-sized connectors and this material has superior adhesiveness to Sn plating in order to decrease contact resistance between male and female terminals and improve corrosion resistance.
However, Cuxe2x80x94Fexe2x80x94P copper alloys, which are conventional materials of connectors, are superior in formability, but have a problem that their spring limit value is low and their resistance property of stress relaxation is poor. In alloys wherein Mg is added to such alloys, their spring limit value is improved but their formability and electric conductivity are lowered. Cuxe2x80x94Mgxe2x80x94P copper alloys are superior in resistance property of stress relaxation but are poor in formability and adhesiveness to Sn plating.
In the light of such problems in the prior art, the present invention has been made. An object of the present invention is to provide a copper alloy for electrical or electronic parts which has superior yield strength, electric conductivity, spring limit value, resistance property of stress relaxation, bendability and Sn plating property.
The copper alloy for electrical or electronic parts of the present invention comprises Fe: 0.5-2.4% (xe2x80x9c%xe2x80x9d means xe2x80x9c% by massxe2x80x9d, which is the same hereinafter.), Si: 0.02-0.1%, Mg: 0.01-0.2%, Sn: 0.01-0.7%, Zn: 0.01-0.2%, P: less than 0.03%, Ni: 0.03% or less, and Mn: 0.03% or less, and further comprises Cu and inevitable impurities as the balance of the alloy.
If necessary, the copper alloy for electrical or electronic parts of the present invention may comprise Pb: 0.0005-0.015%, and/or may comprises one or more of Be, Al, Ti, V, Cr, Co, Zr, Nb, Mo, Ag, In, Hf, Ta and B in their total amount of 1% or less.
The amount of each of Bi, As, Sb and S as the inevitable impurities of the copper alloy is set up to 0.003% or less, and the total amount of these impurities is set up to 0.005% or less from the viewpoint of the production of the copper alloy. From the viewpoint of the same, the amount of O is preferably limited to 10 ppm or less and the amount of H is preferably limited to 20 ppm or less.
The copper alloy for electrical or electronic parts according to the present invention has all of properties which are required for such electrical or electronic parts as a terminal, a connector, a relay and bus bar. The above-mentioned properties include strength (yield strength), electric conductivity, spring limit value, resistance property of stress relaxation, bendability, and Sn plating property. The copper alloy is especially suitable for wiring materials for cars and in particular for materials of small-sized connectors for supplying electric power.
In the copper alloy for electrical or electronic parts according to the present invention, Si, which has deoxidization effect, is added and the added amount of P, which blocks uniform recrystallization, is made as small as possible. Thus, the copper alloy can be produced at low costs and with high productivity.
Components or composition of the copper alloy for electrical or electronic parts of the present invention will be described hereinafter.
Fe
Fe is precipitated in this copper alloy to improve its strength. However, if Fe is contained in an amount over 2.4%, coarse Fe grains are crystallized or precipitated to lower its bendability. On the other hand, if the amount is below 0.5%, Fe is not easily precipitated to lower the strength and the electric conductivity of the alloy. Moreover, grains of recrystallization grow so that cracks are easily generated upon bending. Therefore, the amount of Fe is set up to 0.5-2.4% and preferably 1.0-2.1%. Within this range, the yield strength and the resistance property of stress relaxation of the alloy are further improved. The amount of Fe is more preferably from 1.8 to 2.0%. Within this range, the effect of suppressing the generation of cracks upon hot-rolling is improved.
Si
Si causes the copper alloy to be deoxidized instead of conventional P (both of Fe and Si contribute to deoxidization). Si has the effect of suppressing recrystallization-blocking-effect of P to promote uniform and fine recrystallization if the amount of P is below 0.03%. Si also has the effect of improving the resistance property of stress relaxation and the spring limit value of the alloy without lowering the electric conductivity thereof very much. If the amount of Si is below 0.02%, these effects are not sufficiently exhibited. On the otherhand, if the amount of Si is over 0.1%, the bendability deteriorates. The amount of Si is therefore from 0.02 to 0.1% and preferably from 0.03 to 0.07%. Within this range, the resistance property of stress relaxation of the alloy is further improved.
Mg
If Mg and solid-solution Sn are co-added to the copper alloy, Mg has the effect of improving its resistance property of stress relaxation and its spring limit value. However, Mg is easily oxidized. If the amount of Mg is large, melting in the atmosphere becomes difficult to lower the electrical conductivity of the alloy. For these reasons, in the copper alloy, Si compensates for a part of effects of Mg and Sn. If the amount of Mg is over 0.2% in the copper alloy (Cuxe2x80x94Fe alloy), uniform recrystallization is blocked so that the bendability of the copper alloy deteriorates. Above all, the resistance property of stress relaxation is not improved if the amount of Mg is below 0.01%. The amount of Mg is therefore set up to 0.01-0.2% and preferably 0.05-0.15%. Within this range, the resistance property of stress relaxation and the spring limit value of the copper alloy are further improved by co-addition of Mg and Sn. If Mg and Sn are not co-added, the resistance property of stress relaxation and the like are not improved.
Sn
If Sn and solid solution Mg are co-added to the copper alloy, Sn has the effect of improving its spring limit value and its resistance property of stress relaxation to a large extent, and improving its bendability. However, if the amount of Sn is over 0.7%, the electric conductivity of the alloy is lowered. Above all, the spring limit value and the bendability thereof are not improved if the amount of Sn is below 0.01%. Therefore, the amount of Sn is set up to 0.01-0.7% and preferably 0.05-0.15%. Within this range, the spring limit value, the resistance property of stress relaxation and the bendability are further improved by the co-addition of Sn and solid solution Mg.
Zn
Zn has a great effect of preventing exfoliation of Sn plating and solder plating. However, if Zn is contained in an amount over 0.2%, Zn is removed and the bendability of the copper alloy also deteriorates. On the other hand, if the amount of Zn is below 0.01%, exfoliation of Sn plating and solder plating is not prevented. The amount of Zn is therefore set up to 0.01-0.2% and preferably 0.1-0.2%. Within this range, the above-mentioned effect is great.
P
P gets mixed as an inevitable impurity. Alternatively, if necessary, P is added to the copper alloy to assist deoxidization and improve its fluidity. However, if the amount of P is large, uniform recrystallization is blocked. The amount of P is therefore setup to less than 0.03% (including 0%). If the amount of P is 0.03% or more, uniform and fine recrystallization texture cannot be obtained in intermediate annealing even if Si is added in an amount of 0.02% or more. In this case, portions which have not yet been recrystallized remain even if the temperature of the intermediate annealing is raised. As a result, the hardness of resultant copper alloy plates is scattered so that the bendability thereof deteriorates. The portions which have not yet been recrystallized cannot be caused to vanish under conditions of annealing ordinarily performed in mass production process even if the number of annealing steps is increased to 2 or more.
The amount of P is preferably set up to 0.005% or less. This is because in copper alloys comprising Fe, Si, Mg and Sn in amounts within the above-mentioned ranges, a peak of an improvement in the electrical conductivity by precipitation of Fe upon intermediate annealing can be made substantially consistent with the finishing of recrystallization of the copper alloy (that is, the recrystallization can be substantially finished when the electric conductivity reaches a peak) by limiting the amount of P within this range. In this way, high electric conductivity and superior bendability can be made compatible.
Ni
Ni gets mixed as an inevitable impurity. Alternatively, if necessary, Ni is added to the copper alloy since Ni has the effect of strengthening grain boundaries therein and preventing the generation of cracks upon hot-rolling. However, if the amount of Ni is over 0.03%, Nixe2x80x94Si intermetallic compounds are produced to lower the resistance property of stress relaxation of the copper alloy. The amount of Ni is therefore set up to 0.03% or less (including 0%).
Mn
Mn gets mixed as an inevitable impurity. Alternatively, if necessary, Mn is added to the copper alloy since Mn has the effect of strengthening grain boundaries therein and preventing the generation of cracks upon hot-rolling. However, if the amount of Mn is over 0.03%, Mnxe2x80x94Si intermetallic compounds are produced to lower the resistance property of stress relaxation of the copper alloy. The amount of Mn is therefore set up to 0.03% or less (including 0%) and preferably 0.01% or less.
Pb
Pb gets mixed as an inevitable impurity. Alternatively, if necessary, Pb is added to the copper alloy to improve machinability and punching quality of the copper alloy. Pb has no effect on respective properties of final product plates. However, if Pb is contained in an amount over 0.015%, Pb is segregated in grain boundaries so that cracks are generated upon hot-rolling. On the other hand, if the amount of Pb is less than 0.0005%, the above-mentioned effect is not exhibited. The amount of Pb is therefore set up to 0.015% or less (including 0%). If the above-mentioned is required, Pb is caused to be contained in an amount of 0.0005% or more.
Be, Al, Ti, V, Cr, Co, Zr, Nb, Mo, Ag, In, Hf, Ta and B
These elements get mixed as inevitable impurities. Alternatively, if necessary, they are added to the copper alloy since they have the effect of raising recrystallization temperature and improving the resistance property of stress relaxation. However, if these elements are precipitated or crystallized, the electric conductivity of the copper alloy is lowered. Therefore, the total amount thereof is limited to 1% or less and preferably 0.5% or less.
Bi, As, Sb, S, O and H
These elements get mixed as inevitable impurities. Since Bi, As, Sb and S are segregated in grain boundaries to generate cracks upon hot-rolling, the amount of each of them is preferably limited to 0.003% or less and the total amount thereof is preferably limited to 0.005% or less. If the amount of O or H is large, blow holes are generated in the ingot. If the amount of O is large, a large amount of oxides is produced in the melt to block the fluidity of the melt. Therefore, the amount of O is preferably limited to 10 ppm or less, and the amount of H is preferably limited to 20 ppm or less.